After my old home built rig died I built another. Speedtest.net consistantly showed at least 75/75 with old rig and new one was 85mb down and only 35mb-40mb upload. Having seen this in the past I explored. Old rig used onboard Atheros network interface card (aka 'NIC'), new rig has onboard Realtek NIC.
Problem: Slow upload speeds but only after computer has been unused for a period of time. We all do this.
Note: Every single Windows install by default has "'Power Management" turn off the NIC when not in use. To disable NIC power down go to driver properties "Power Management" tab and uncheck all boxes.
After ruling out the obvious - Your PC, Router and Verizon tests, and have flushed your browser cache and DNS, here is the most likely problem causing intermittent slow upload speeds:
TEST 1: Upon complete computer reboot (not sleep or hibernate) up and download
speeds are ok.
SYMPTOM: Computer first powers down (after whatever minutes power settings are set
at) and is then woken up.
1) Newer Realtek NIC drivers have three settings of interest under the 'Advanced' tab.
1a) "Energy Efficient Ethernet" Default is 'Enabled'. Set to 'Disabled'.
1b) "Green Ethernet" Default is 'Enabled'. Set to 'Disabled'.
1c) "WOL & Shutdown Link Speed" Default is "10 mbps First" Set to "Not Speed
Down".
2) Problem occurs when computer sits unused then NIC powers up again to the "10
Mbps First".
3) Though the NIC will eventually uprate to higher speed, it will start at lower rate thus
causing the problem.
4) My old Atheros NIC driver did not have the driver settings to save power and the
Realtek one did.
5) Other NIC manufacturers may or may not have driver based power settings. At the
very least go in the "Power Management" settings and uncheck boxes so NIC never
powers down.
Common problem many do not think of in todays 'instant gratification' society. This happened way back in Win 3.11/95 days and continues to this day in all Windows OS's.
Hopefully others find this useful. And yes I shared this with Tech Support for their peer review process. Even if this works for some not all this is a common problem many tend to forget.
~Peace